Wis. Stat. § 74.10: Agreements on payments.

A county and a taxation district in that county may contract under s. 66.0301 for the county to receive all payments of property taxes for which the taxation district has sent bills under s. 74.09. A contract under this section may provide for reimbursement to the county of its expenses and shall provide for prompt deposit of the amounts collected into an account of the taxation district and for possession by the taxation district of the interest credited to that account.